This invention concerns end of travel arrangements associated with a carriage for an ergo assist arm, used at workstations located along an assembly line to assist lifting and positioning of parts to be installed or for performing other operations. The end of travel arrangement stops an assembly line conveyor if the carriage reaches a predetermined limit in its range of motion alongside the assembly line.
Each ergo assist arm is typically supported on an associated carriage mounted on a pair of runway rails extending along one side of an assembly line conveyor, the carriage being movable along the runway rails so as to be able to move along with the auto body moved by the assembly line conveyor so as to be able to conduct an assembly or other operation on the moving auto body.
The ergo assist arm is disposed to enable an assembly line worker to carry out a particular operation while the carriage supporting the ergo assist arm is being moved parallel to the assembly line to match the motion of the auto body down the line. As a practical matter, there is a limited range of movement of the carriage and ergo assist arm along the runway rails, and the carriage will eventually reach an end of travel position if the assembly step or other operation is not completed in the normal interval allowed.
This is because the assembly line conveyor is continuously operated, and the auto body or other work will eventually advance beyond the limited range of travel of the ergo assist arm carriage.
This will cause the assembly line conveyor to pull the ergo assist arm from the station and possibly damaging the same.
Also, the auto body being assembled must not be advanced downstream to other stations along the assembly line where other assembly steps are to be carried out if an earlier assembly operation has not been completed in an upstream station.
For this reason, an end of travel arrangement has hereto been provided which is designed to stop the assembly line conveyor if movement of the carriage along the runway rails past a predetermined travel limit is detected. The end of travel arrangements have included one or more limit switches which when tripped sound an alarm when the end of travel arrangement trolley begins to exceed the limit of its normal range of motion. The assembly line conveyor control also receives a signal from a limit switch initiating a stoppage of the assembly line conveyor which stops after the inertia of assembly line motion is dissipated. The continuous nature of the alarm commonly leads to efforts by plant personnel in an attempt to disable the switches to turn off the alarm, often damaging the switches in the effort.
In these prior designs using mechanical limit switches, a dog feature on the carriage engages and trips the limit switch when the carriage reaches the designed for end of travel point, to thereby detect such over travel occurrence.
Since such limit switches have a trip element which is mechanically engaged in order to be operated, over time deformation of the trip element can result in a failure of the carriage dog feature to make contact with the switch trip element and result in a failure of the end of travel arrangement to shut down the assembly line conveyor when over travel occurs.
As noted above, vigorous efforts are often attempted after the alarm has sounded to physically deactivate the switch as with a pole or broom handle. The limit switches are typically mounted in an exposed location since a mechanical engagement with the switch trip element is necessary, and thus, vigorous efforts such as banging on the exposed limit switches by assembly line workers sometimes occur, often resulting in damage to the limit switches to the extent that the end of travel arrangement becomes inoperative. Extensive repairs and an extended assembly line shutdown may then be necessary.
In some situations, it would be desirable to allow continued limited manual movement of an ergo assist arm carriage by a substantial advance of the carriage after an automatic shutdown of the assembly line has occurred, as to enable repositioning a part carried by the ergo assist arm in order to prepare for a restart of the assembly line conveyor.
It is an object of the present invention to provide a more reliable and durable end of travel arrangement for automatically shutting down an assembly line conveyor when over travel of the carriage supporting the ergo assist arm is detected.
It is a further object to provide an end of travel arrangement which is shielded against being damaged by any attempt to interfere with an end of travel detection switch.
It is yet another object to provide an end of travel arrangement which allows a substantial manual movement of the ergo assist arm support carriage after a conveyor shut down so as to enable repositioning of the ergo assist arm after the conveyor has been shut down.